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US-12628565-B2 - Piezoelectric device having electrode formed of amorphous oxide conductor

US12628565B2US 12628565 B2US12628565 B2US 12628565B2US-12628565-B2

Abstract

A piezoelectric device that exhibits good piezoelectric characteristics, while reducing generation of leakage current paths, and a method of manufacturing the same, are provided. The piezoelectric device has a multilayer stack in which a first electrode, a piezoelectric layer, and a second electrode are stacked in this order on a substrate, wherein at least the first electrode is formed of an amorphous oxide conductor.

Inventors

  • Naoki Nagaoka
  • Daisuke Nakamura
  • Manami KUROSE

Assignees

  • NITTO DENKO CORPORATION

Dates

Publication Date
20260512
Application Date
20190926
Priority Date
20180928

Claims (11)

  1. 1 . A piezoelectric device comprising: a multilayer stack in which a first electrode, a piezoelectric layer, and a second electrode are stacked in this order on a substrate, wherein the piezoelectric layer has a wurtzite crystal structure, the piezoelectric layer consists of one type of a piezoelectric material located between the first electrode and the second electrode, the piezoelectric layer is in direct contact with the first electrode, at least the first electrode is formed of an amorphous oxide conductor, the first electrode is formed of a material selected from a group consisting of IZO, IZTO, and IGZO, and a thickness of the first electrode is 10 nm or more.
  2. 2 . The piezoelectric device as claimed in claim 1 , wherein the thickness of the first electrode is 10 nm to 200 nm.
  3. 3 . The piezoelectric device as claimed in claim 2 , wherein the thickness of the first electrode is 10 nm to 100 nm.
  4. 4 . The piezoelectric device as claimed in claim 1 , wherein the piezoelectric layer is formed of a material selected as a main component from a group consisting zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), aluminum nitride (AlN), gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), silicon carbide (SiC), and combinations thereof.
  5. 5 . The piezoelectric device as claimed in claim 4 , wherein the piezoelectric layer contains a subcomponent in the main component, the subcomponent is a material selected from a group consisting of magnesium (Mg), vanadium (V), titanium (Ti), zirconium (Zr), silicon (Si), lithium (Li), and combinations thereof.
  6. 6 . The piezoelectric device as claimed in claim 1 , wherein a d33 value of the piezoelectric layer ranges from 2.2 to 5.0 pC/N.
  7. 7 . The piezoelectric device as claimed in claim 1 , wherein the substrate is formed of a plastic or a resin.
  8. 8 . The piezoelectric device as claimed in claim 1 , wherein the second electrode is formed of an amorphous oxide conductor.
  9. 9 . A method of manufacturing a piezoelectric device, the method comprising: forming a first electrode on a substrate, the first electrode being formed of an amorphous oxide conductor; forming a piezoelectric layer having a wurtzite crystal structure on the first electrode; and forming a second electrode on the piezoelectric layer, wherein the piezoelectric layer consists of one type of a piezoelectric material located between the first electrode and the second electrode, the piezoelectric layer is in direct contact with the first electrode, the first electrode is formed of a material selected from a group consisting of IZO, IZTO, and IGZO, and a thickness of the first electrode is 10 nm or more.
  10. 10 . The method as claimed in claim 9 , wherein the first electrode is formed by sputtering at room temperature on a plastic substrate or a resin substrate.
  11. 11 . The method as claimed in claim 9 , wherein during formation of the first electrode, a ratio of an oxygen flow to a total flow of argon gas and the oxygen falls within a range of 0% to 2.0%.

Description

CROSS REFERENCE TO RELATED APPLICATION This application is a National Stage of International Application No. PCT/JP2019/037942, filed on Sep. 26, 2019, which designates the United States and was published in Japan, and which is based upon and claims priority to Japanese Patent Application Nos. 1) 2018-185548, filed on Sep. 28, 2018; and 2) 2019-173384, filed on Sep. 24, 2019 in the Japan Patent Office. All of the aforementioned applications (including the earlier-filed Japanese Patent Applications) are hereby incorporated by reference in their entireties. TECHNICAL FIELD The present invention relates to a piezoelectric device and a method of manufacturing the same. BACKGROUND ART Piezoelectric devices, which make use of the piezoelectric effect of substances, have conventionally been adopted. The piezoelectric effect is a phenomenon in which microscopic polarization is produced in response to a mechanical stress applied to a substance. Using the piezoelectric effect, various sensors including pressure sensors, acceleration sensors, and acoustic emission 36256AE) sensors for detecting elastic waves are commercially available. Piezoelectric devices are typically formed into a multilayer stack with a piezoelectric layer sandwiched between a pair of electrodes. A structure having electrode films made of a metal alloy such as Ti-alloy, Mg-alloy, Al-alloy, Zn-alloy or the like is proposed. With this structure, the Young's modulus of the electrode films is set smaller than that of the piezoelectric layer. See, for example, Patent Document 1 presented below. It is described in this document that the electrode films preferably have an unoriented or amorphous structure. SUMMARY OF THE INVENTION Technical Problem to be Solved A multilayer stack with a piezoelectric layer sandwiched between a pair of electrodes is generally fabricated on a substrate, from the viewpoint of structural stability and convenience of fabrication approach. When a plastic or resin substrate is used, the surface of the substrate tends to be rough or uneven. Such surface roughness or unevenness of the substrate is hardly absorbed by the metal crystal of the subsequently formed electrode, and in fact, the surface of the metal electrode formed on the uneven substrate becomes uneven. The unevenness or pinholes present in the metal surface may cause cracks in a piezoelectric layer formed over the metal film, and leakage current paths may be created between the top and bottom electrodes. Such leakage current paths diminish the electric charges produced by polarization and accumulated at the interfaces of the piezoelectric layer, and consequently, the piezoelectric effect may not be exhibited. One of the objectives of the present invention is to suppress a leakage current path and provide a piezoelectric device having a satisfactory piezoelectric characteristic and a method of manufacturing the same. Technical Solution(s) In one aspect of the invention, one or both of a pair of electrodes is formed of an amorphous oxide conductor. In particular, a piezoelectric device includes a first electrode, a piezoelectric layer, and a second electrode stacked in this order on a substrate, wherein at least the first electrode is formed of an amorphous oxide conductor. In an example configuration, the thickness of the first electrode may range from 10 nm to 200 nm, and more preferably, 10 nm to 100 nm. Advantageous Effect of the Invention With the above-described configuration, the leakage current path can be suppressed, and a piezoelectric device with a satisfactory piezoelectric characteristic can be achieved. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram of a piezoelectric device according to an embodiment; FIG. 2 is a schematic diagram of a sample used for characteristic evaluation; FIG. 3 illustrated how piezoelectric coefficient d33 values are measured; FIG. 4 shows measurement results of the samples; FIG. 5 shows measurement results of comparative structures; FIG. 6 illustrates how the piezoelectric characteristics deteriorate when a metal electrode film is provided under the piezoelectric layer; and FIG. 7 shows small-angle X-ray diffraction measurement results of samples prepared under different flow ratios of O2 to Ar. DESCRIPTION OF PREFERRED EMBODIMENTS In general, when a piezoelectric layer is formed of a wurtzite material such as zinc oxide (ZnO), it is believed that depositing a crystal film under the piezoelectric layer is desirable because a wurtzite layer can be grown with a good crystal orientation, reflecting the underlayer crystal structure. It is also assumed that the piezoelectric layer should have a certain degree of thickness in order to secure the crystal orientation of the piezoelectric layer. However, increasing the thickness of the piezoelectric layer tends to cause cracking or crazing in the piezoelectric layer. In particular, when the surface of the underlaid metal electrode is uneven, cracks or pinholes are likely to a